All About Direct Metal Laser Sintering (DMLS) 3D Printing

A DMLS 3D printer is a powder-bed fusion technology. It is used to manufacture metal parts by directing a high-powered fiber laser beam at a single, thin layer of metal powder and fusing an outline of that layer onto the previous layers. The process is repeated for every successive layer until the entire metal part has been printed, one layer at a time, with each layer melted into the previous one. The term Direct Metal Laser Sintering (DMLS) was coined in 1995 when a German company called EOS (Electro Optical Systems) first commercialized it. EOS also owns the DMLS trademark.
The word "sintering" in DMLS is actually somewhat of a misnomer. Sintering involves heating a powdered material to the point where it coalesces into a solid mass without melting the material. According to EOS, DMLS is a German acronym that stands for “Direkt Metall Laser Schmelzen.” Schmelzen'' means "melt," not "sinter." Despite the English name of the process, Direct Metal Laser Sintering does not actually involve sintering the metal powder. Instead, it melts the metal particles together to form the part. This is why the process is also sometimes referred to as Direct Metal Laser Melting (DMLM).

Direct Metal Laser Sintering (DMLS) is used for the serial manufacture of complex industrial metal components that cannot be made economically—or at all—with other metal manufacturing technologies, such as CNC machining or metal injection molding. It's one of our most important 3D printing processes at Xometry. When parts are manufactured using traditional subtractive processes, they often need to be assembled from multiple components. However, DMLS 3D printing can create a monolithic part that eliminates the inherent weaknesses and complexities of assembled parts. DMLS printing is most often used in the aerospace, medical, turbomachinery, and automotive industries.

Common materials used in DMLS printing include:

1. Aluminum Alloys (AlSi10Mg): This aluminum alloy is typically used for casting applications. It can be used on components with thin walls and fine features. This alloy also has good mechanical and thermal properties.
2. Inconel® 718: Inconel® is a nickel superalloy often used in the aerospace industry, where it is useful for its ability to maintain high strength at extremely high temperatures. It is also highly corrosion resistant. 
3. Titanium (Ti6Al4V): This titanium alloy has excellent mechanical and corrosion resistance properties. In addition, it is biocompatible, making it ideal for medical implants.
4. Stainless Steel (316L): 316L is a very corrosion-resistant material. It is used extensively in industrial acid-producing facilities, specifically in handling sulphuric acid.
5. Copper: Copper has excellent thermal and electrical conductivity. It is often used for heat exchangers and induction coils. Copper (Cu) and some copper alloys like CuCP and CuCrZr can be printed on DMLS printers.
6. Case-Hardening Steel (20MnCr5): This material can be case hardened after printing. That makes it ideal for applications requiring superior wear resistance, such as gear wheels.
7. Cobalt-Chrome (CoCr): This  CoCr alloy family has excellent corrosion resistance and maintains its mechanical properties at elevated temperatures. It is a nickel-free alternative to Inconel®. It is also biocompatible and used for components in gas turbines and orthopedic implants. 

Direct Metal Laser Sintering is one of the most mature and efficient metal printing technologies. Listed below are some of its key advantages:

1. DMLS is capable of printing high-strength functional metal parts in a wide variety of metals.
2. It is possible to print mixtures of plastic (nylon) and metal (aluminum).
3. DMLS is a high-resolution printing process that can produce very small feature sizes. This is because the DMLS laser beam can be as narrow as 40 micrometers.

Disadvantages:

1. DMLS parts need support during printing. This is due to the mass of the metal parts.
2. DMLS parts can have internal stresses due to the high-temperature manufacturing process. Removing these internal stresses during printing requires multiple test samples and additional characterization. Alternatively, post-print heat treatment can also remove these stresses. However, both of these processes ultimately result in a higher cost per part.
3. DMLS makes use of lower-powered lasers compared to SLM and EBM machines. Therefore, it produces a smaller melt pool and cannot print very high layers. This ultimately results in slower prints and, therefore, higher cost per part.

Differences Between DMLS and SLM 3D Printing

Both DMLS and SLM are powder-bed fusion printing technologies. SLM makes use of higher-power lasers, can handle bigger parts, and can incorporate up to 12 lasers. Thus, SLM is better suited to high-volume production, whereas DMLS is better suited to smaller volumes and more highly detailed parts. For more information, see our guide on DMLS vs. SLM 3D Printing.